Treatment fluids comprising starch and ceramic particulate bridging agents and methods of using these fluids to provide fluid loss control

ABSTRACT

Compositions relating to fluid loss control operations are provided. In some embodiments, fluid loss treatment fluid compositions are provided that may comprise ceramic particulate bridging agents, wherein at least a portion of the ceramic particulate bridging agents comprise chemically bonded particulates, a partially depolymerized starch derivative, and a base fluid are provided. In other embodiments, fluid loss treatment fluid compositions are provided comprising ceramic particulate bridging agents, wherein at least a portion of the ceramic particulate bridging agents are substantially insoluble in water; a partially depolymerized starch derivative, and a base fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of commonly-owned U.S. patentapplication Ser. No. 11/329,345, now U.S. Pat. No. 7,211,548, filed Jan.10, 2006, entitled “Treatment Fluids Comprising Starch and CeramicParticulate Bridging Agents and Methods of Using These Fluids to ProvideFluid Loss Control,” by Trinidad Munoz, Jr., et al., which is in turn adivisional of U.S. patent application Ser. No. 10/657,988, now U.S. Pat.No. 7,036,588, filed Sep. 9, 2003, entitled “Treatment Fluids ComprisingStarch and Ceramic Particulate Bridging Agents and Methods of UsingThese Fluids to Provide Fluid Loss Control,” which is incorporated byreference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to fluid loss control operations. Moreparticularly, the present invention provides compositions comprisingceramic particulate bridging agents and improved fluid loss controladditives, and methods of using those compositions to provide fluid losscontrol.

Drilling and servicing fluids, inter alia, deposit filter cake on thewalls of well bores within the producing formations to substantiallyprevent drilling, servicing, and completion fluids from being lost intothe formation and solids from entering into the porosities of theformation. After the drilling or servicing operation has been completed,the filter cake is removed prior to placing the formation on production.Removal of the filter cake heretofore has been accomplished by includinga water, oil, or acid soluble particulate solid bridging agent in thetreatment fluid for bridging over the formation pores or other opening.Such areas include formation pore throats, gravel packs, sand screens,or fractures in the formation as well as openings such as cracks intubing or casing, holes in sand screens, or on other perforationsdownhole such as in a shroud, casing, or other tubing. By bridgingacross such areas, the bridging agents combined with a fluid losscontrol additive form a substantially impermeable “filter cake” on thatarea that prevents loss of treatment fluids to the surroundingformation.

Common bridging agents include calcium carbonate, suspended salts, oroil-soluble reins. For lost-circulation treatments outside theproduction interval, any suitably sized product may be used, includingmica, nutshells, and fibers. The selection of an appropriate bridgingmaterial is more critical in the production interval and duringwork-over operations since the barrier should be completely removed inpreparation for placing the well back into production. As an alternativeto conventional bridging agents, chemically bonded ceramic particulatesare desirable because they are customizable as these particulates aremade via a process similar to that of mixing a cementitious material. Asa result, their composition, and properties can be varied, and they canbe impregnated with desirable additives. Another advantageous feature ofthese particular bridging agents is that they are soluble in ammoniumsalts and chelating agents.

Starches are often used in conjunction with bridging agents, inter alia,to aid in the prevention of fluid loss to the formation. Starches arecarbohydrates of a general formula (C₆H₁₀O₅)_(n), and are derived fromcorn, wheat, oats, rice, potatoes, yucca, and the like. Most starchesusually comprise about 27% linear polymer (amylose) and about 73%branched polymer (amylopectin). These two polymers are intertwinedwithin starch granules. Granules generally are insoluble in cold water,but soaking in hot water or under steam pressure ruptures their coveringand the polymers hydrate into a colloidal suspension. Amylose andamylopectin are nonionic polymers that do not interact withelectrolytes. Derivatized starches, such as hydroxy propyl andcarboxylmethyl starches are used in drill-in fluids, completion fluids,and various brine systems as well as in drilling fluid systems.

Problems arise, however, when conventional starches are added to fluidscomprising chemically bonded ceramic particulates. When combined, thefluid gels to a point where it ultimately has the consistency of paste.As a result, this combination is unusable in downhole applications. Thisis unfortunate because the starch provides an added means to ensurefluid loss control in a process using the desirable chemically bondedceramic particulates.

SUMMARY OF THE INVENTION

The present invention relates to fluid loss control operations. Moreparticularly, the present invention provides compositions comprisingceramic particulate bridging agents and improved fluid loss controladditives, and methods of using those compositions to provide fluid losscontrol.

In one embodiment, the present invention provides a fluid loss treatmentfluid comprising ceramic particulate bridging agents, wherein at least aportion of the ceramic particulate bridging agents comprise chemicallybonded particulates, a partially depolymerized starch derivative, and abase fluid.

In another embodiment, the present invention provides a fluid losstreatment fluid comprising ceramic particulate bridging agents, whereinat least a portion of the ceramic particulate bridging agents aresubstantially insoluble in water; a partially depolymerized starchderivative, and a base fluid.

The objects, features and advantages of the present invention will bereadily apparent to those skilled in the art upon a reading of thedescription of the preferred embodiments that follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to fluid loss control operations. Moreparticularly, the present invention provides compositions comprisingceramic particulate bridging agents and improved fluid loss controladditives, and methods of using those compositions to provide fluid losscontrol. Even more particularly, the present invention provides improvedtreatment fluids, including drilling as well as servicing fluids thatcomprise ceramic particulate bridging agents and a modified starchcomposition to deposit filter cakes that can readily be removed withoutthe use of strong acids or other hazardous chemicals that may createproblems on the well site, e.g., equipment corrosion. The treatmentfluids of the present invention may be formulated to bridge on anydesired opening where it is desirable to control fluid loss. Insubterranean applications this may include any opening within a wellborepenetrating a subterranean formation such as a gravel pack, a screen, aperforated shroud, a portion of the subterranean formation, or any otheropening such as a crack in the casing or other tubing within the hole.

The treatment fluids of the present invention comprise ceramicparticulate bridging agents, a modified starch fluid loss additive, anda base fluid. The combination of the modified starches and the ceramicbridging agents of the present invention provides a beneficial means tocontrol fluid loss where desirable. Heretofore known combinations ofconventional starches and ceramic bridging agents have resulted inunusable compositions. Optionally, the treatment fluids of the presentinvention may comprise a viscosifier. The treatment fluids of thepresent invention may be used when there is risk of undesirable fluidloss, for example, into the subterranean formation surrounding a wellbore. Examples of fluids in which the treatment fluids of the presentinvention may be used include drilling fluids, drill-in fluids, andfluid loss control pills. Other examples include servicing andcompletion fluid applications. Optionally, other components such asviscosifiers, salts, surfactants, clay control additives, lubricants,biocides, and the like may be included within the treatment fluidcompositions of the present invention. One of ordinary skill in the artwith the benefit of this disclosure will recognize when such optionalcomponents should be included.

The ceramic particulate bridging agents and modified starches of thepresent invention act to form a filter cake in the subterraneanformation, inter alia, to prevent or eliminate fluid loss from the wellbore to the formation. In certain embodiments of the present inventionwhen used in a subterranean application, the ceramic particulatebridging agents and modified starches are deposited by the treatmentfluid on the walls of the well bore in the producing zone being drilledor serviced along with other components. These ceramic particulatebridging agents and modified starches may be added to the treatmentfluids of the present invention, inter alia, to bridge across anyopening for which fluid loss control is desired. In certain embodiments,this may include the pore throats, fractures of an exposed rock, orother undesirable openings extending from the well bore into aformation. The bridging agents in effect plug off fluid paths from onelocation to another. The bridge may be partial or total. To build a sortof filter cake on those openings, the bridging agents and modifiedstarches may lodge together or otherwise cohesively create a barrier tofluid flow.

The ceramic particulate bridging agents of the present invention arepreferably chemically bonded particulates. Such chemically bondedparticulates are preferred because they have an inherent flexibility intheir composition, properties, and in their ability to act as carriersfor desirable additives such as breakers. Any ceramic particulatebridging agent that is compatible with the conditions of the proposedapplication is suitable for use in conjunction with the presentinvention. In certain preferred embodiments, the particulate bridgingagents used in the compositions and methods of the present inventioncomprise inorganic compounds that are substantially insoluble in water,but which are substantially soluble, for example, in aqueous ammoniumsalt clean-up solutions. One example of such suitable magnesium-basedceramic particulate bridging agents include compounds illustrated bythis formula: MgO+KH₂PO₄+5H₂O→MgKPO₄.6H₂O. These materials weredeveloped by Argon National Labs., in Chicago, Ill., and may beavailable from Argon National Labs. under the tradename “CERAMICRETE.”Other examples of suitable particulate bridging agents include compoundsdescribed by these formulae:MgO+H₃PO₄+2H₂O→MgHPO₄.3H₂OMgO+NH₄H₂PO₄+5H₂O→MgNH₄PO₄.6H₂OExamples of ceramic particulate bridging agents that are described bythese formulae are Newberyite, and Struvite, respectively. The ceramicparticulate bridging agent utilized in the treatment fluids of thepresent invention are generally included therein in an amount of fromabout 5% to about 60% by weight of the base fluid component, morepreferably in the range of from about 7% to about 20%, and mostpreferably at around 10%.

The particle size distribution of the ceramic particulate bridgingagents may be varied depending on the openings to which the bridgingagents will be introduced. Generally speaking, the particle sizedistribution of the bridging agents must be sufficient to bridge acrossand seal the desired opening downhole. For example, if the pore throats(i.e., very small openings) on a portion of a subterranean formation areto be bridged, then it would be beneficial to use smaller ceramicparticulate bridging agents. A suitable size range for this type ofapplication would range from about 0.1 microns to about 200 microns. Inother applications, larger bridging agent particulates will beappropriate, for example, when bridging on a gravel pack. Suitable sizeranges for such applications include about 1 micron to about 1millimeter. In other applications, the particle size range may be fromabout 5 microns to about 8 millimeters. This range may be preferredwhen, for example, the operation involves sealing on perforations orother openings, such as objects having a plurality of holes.

In certain preferred embodiments, the ceramic particulate bridgingagents of the present invention are impregnated with, coated with, orotherwise incorporate a desirable additive. Such desirable additivesinclude but are not limited to polymer breakers, scale inhibitors,weighting agents, paraffin inhibitors, and the like. In one embodimentof the present invention, a breaker is added to the ceramic mixture asthe mixture is being formed into particulate bridging agents. When it isdesirable to remove them, these breakers are released and, inter alia,may reduce the viscosity of a viscosified treatment fluid or breakstarch or xanthan in a filter cake. One of ordinary skill in the artwith the benefit of this disclosure may recognize other additives thatmay be beneficially employed with the particulate bridging agents for agiven application.

The modified starch compositions of the present invention provideenhanced fluid loss control when used in conjunction with ceramicbridging agents and preferably comprise modified starches. Generally,these starches may be a crosslinked ether derivative of a partiallydepolymerized starch and/or a partially depolymerized crosslinked etherderivative of a starch. In the former case, the starch is partiallydepolymerized prior to crosslinking and derivatizing the starch, whereasin the latter case the starch is first crosslinked and derivatized priorto partially depolymerizing the starch derivative. In either case, themolecular weight of the crosslinked starch derivative is decreased bythe partial depolymerization of the starch polymer. As used herein, theterms “partially depolymerized starch derivative” and “hydrolyzed starchderivative” are intended to mean the starch derivatives prepared byeither method.

In certain embodiments where a crosslinked ether derivative of apartially depolymerized starch is used, it is preferred that the starchbe hydrolyzed or depolymerized to the extent that the viscosity of anaqueous dispersion of the starch is reduced about 25% to about 92%,preferably about 50% to about 90%, prior to crosslinking andderivatizing the starch. In the second case, i.e., a partiallydepolymerized crosslinked ether derivative of a starch, it is preferredthat the crosslinked derivative starch by hydrolyzed or depolymerized tothe extent that the viscosity of the water dispersion of the starchderivative at a concentration of about 60 kg/m³ is reduced by about 15%to about 50%, preferably 20% to about 40%. An example of a suitablestarch is BROMA FLA™, commercially available from TBC Brinadd ofHouston, Texas.

In some embodiments, the modified starch composition is included withinthe treatment fluid compositions of the present invention in a range offrom about 0.1% to about 3% by weight of the base fluid component, morepreferably in a range of from about 1% to about 1.5%, and mostpreferably about 1.3% of the base fluid component.

A variety of viscosifiers are suitable for use in conjunction with thepresent invention. These include, but are not limited to, biopolymerssuch as xanthan and succinoglycan, cellulose derivatives such ashydroxyethylcellulose, and guar and its derivatives such ashydroxypropyl guar. One of ordinary skill in the art with the benefit ofthis disclosure will recognize other suitable viscosifiers that may beused in conjunction with the present invention. Xanthan is preferred.The viscosifier is generally included in the treatment fluidcompositions of the present invention in an amount ranging from about 0%to 1.0% by weight of the base fluid component. In certain preferredembodiments, the viscosifier is included in the composition in an amountranging from about 0.13% to about 0.16%. One of ordinary skill in theart with the benefit of this disclosure will be able to determine theappropriate amount of viscosifier needed for a given application.

The base fluid component of the treatment fluid compositions of thepresent invention preferably comprises an aqueous component. Suitableexamples include water, brine, salt water, and the like. Oil-basedfluids generally are not the most suitable base fluids for thesecompositions because they may negatively affect the performance of thestarch.

In certain embodiments when the present invention is used in asubterranean application, once the drilling or servicing operation hasbeen completed, a clean-up solution comprising water and a solubilizingagent is introduced into the wellbore whereby the ceramic particulatebridging agents in the filter cake are dissolved. Suitable solubilizingagents include ammonium salts and chelating agents. Suitable ammoniumsalts include ammonium salts have the following formula:R_(n)NH_(4-n)Xwherein R is an alkyl group having from 1 to 6 carbon atoms, n is aninteger from 0 to 3 and X is an anionic radical, for example, halogens,nitrates, citrates, acetates, sulfates, phosphates, and hydrogensulfates. Examples of suitable such ammonium salts include but are notlimited to ammonium chloride, ammonium bromide, ammonium nitrate,ammonium citrate, ammonium acetate, and mixtures thereof. Of these,ammonium chloride is preferred. The ammonium salt is usually included inthe clean-up solution in an amount ranging from about 3% to about 25% byweight of the water therein, more preferably in the range of from about5% to about 14% and most preferably about 5%. As for chelating agents,the term “chelating agent” as used herein is used to mean a chemicalthat will form a water-soluble complex with the cationic portion of thebridging agent to be dissolved. Various chelating agents can be utilizedincluding but not limited to ethylenediaminetetraacetic acid and saltsthereof, diaminocyclohexanetetraacetic acid and salts thereof,diglycolic acid and salts thereof, citric acid and salts thereof,nitroilotriacetic acid and salts thereof, phosphonic acid and saltsthereof, and aspartic acid and salts thereof. Of these, citric acid ispreferred. The chelating agent utilized is generally included in theclean-up solution in an amount in the range of from about 0.1% to about40% by weight of the solution, more preferably in the range of fromabout 5% to about 20%, and most preferably around 20%. Optionally, theclean-up solution may include one or more oxidizers or other breakersfor oxidizing and breaking up various components of the filter cake whendesired.

After the drilling or servicing of the producing formation has beencompleted, the clean-up solution is introduced into the producingformation into contact with the filter cake deposited therein. Theclean-up solution is allowed to remain in contact with the filter cakefor a period of time sufficient for desired components in the filtercake to be broken up and the bridging agents to be dissolved. The timewith which the solubilizing component of the clean-up solution dissolvesthe components in the filter cake may vary. For example, thisinteraction could intentionally be a delayed interaction such that thedegradation of the filter cake is delayed. A delayed break of the filtercake can be achieved by utilizing a chelating agent such as sodiumdiglycolate that does not dissolve the bridging agents out of thepresence of the ammonium salt or salts. The ammonium salts can bedelivered in a form designed to release them after a chosen time delay.At that release point, the chelating agent will act to begin to degradethe bridging agents in the filter cake. In other embodiments, theinteraction may be immediate. If desired, a wash solution can be used toremoving any remaining filter cake.

An embodiment of the present invention provides a method of providingfluid loss control through an opening from a first location to a secondlocation comprising the steps of: providing a treatment fluid comprisingceramic particulate bridging agents, a modified starch composition, anda base fluid; introducing the treatment fluid to the first location; andallowing the treatment fluid to form a filter cake to prevent fluid lossfrom the first location to the second location.

EXAMPLES

Table 1 shown below is the drill-in fluid mud recipe using Newberyiteand a commonly used starch. The starch used in this recipe was a starchknown as “N-DRIL HT PLUS,” which is a commonly used starch availablefrom Halliburton Energy Services in various locations. N-DRIL HT PLUS isa stabilized nonionic starch derivative (waxy maize) that seeks tocontrol high pressure, high temperature filtrate loss. In combinationwith other polymers such as xanthan, N-DRIL HT PLUS is synergistic andyields improved suspension. However, when used in combination withceramic bridging agents, the combination will form a poor filter cakeand will become a thick gel.

TABLE 1 Component Amount 10% NaC1 336 ml Xanthan 0.85 g N-DRIL HT PLUS7.4 g Newberyite 25.0 g NaOH 0.1 g

The composition of Table 1 formed a thick gel that was not usable insubterranean applications.

Table 2 shown below is the drill-in fluid mud recipe using Newberyiteand a modified starch as those starches are described herein. Thiscomposition forms a tight filter cake, and does not form an unusablethick gel, even over a 24 to 48 hour period. The starch used in thisrecipe is BROMA FLA™, which is commercially available from TBC Brinaddof Houston, Texas.

TABLE 2 Component Amount Water 317 ml NaCl 90.4 g BROMA FLA ™ 5.0 gXanthan 1.25 g Newberyite 25.0 g

1. A fluid loss treatment fluid comprising: ceramic particulate bridgingagents, wherein the ceramic particulate bridging agents comprise atleast one ceramic particulate bridging agent described by at least oneof the following formulae:KH₂PO₄+5H₂O →MgKPO₄6H₂O;MgO +H₃PO₄ +2H₂O →MgHPO₄ 3H₂O; andMgO +NH₄H₂PO₄ +5H₂O →MgNH₄PO₄ 6H₂O, a partially depolymerized starchderivative, and a base fluid.
 2. The composition of claim 1 wherein thefluid loss treatment fluid is a component of a drilling fluid, adrill-in fluid, or a fluid loss control pill.
 3. The composition ofclaim 1 wherein the treatment fluid further comprises an additivewherein the additive is a viscosifier, a salt, a surfactant, a claycontrol additive, a lubricant, or a biocide.
 4. The composition of claim1 wherein the ceramic particulate bridging agents comprise a magnesiumcompound.
 5. The composition of claim 1 wherein the ceramic particulatebridging agents are included in the treatment fluid in an amount rangingfrom about 5% to about 60% based on the weight of the base fluid.
 6. Thecomposition of claim 1 wherein the ceramic particulate bridging agentshave a particle size distribution ranging from about 0.1 microns toabout 200 microns.
 7. The composition of claim 1 wherein the ceramicparticulate bridging agents have a particle size distribution rangingfrom about 1 micron to about 1 millimeter.
 8. The composition of claim 1wherein the ceramic particulate bridging agents have a particle sizedistribution ranging from about 5 microns to about 8 millimeters.
 9. Thecomposition of claim 1 wherein at least a portion of the ceramicparticulate bridging agents comprise an additive chosen from the groupconsisting of a breaker, a scale inhibitor, a weighting agent, and aparaffin inhibitor.
 10. The composition of claim 1 wherein the partiallydepolymerized starch derivative is a crosslinked ether derivative of apartially depolymerized starch.
 11. The composition of claim 1 whereinthe modified starch composition is included in the treatment fluid in anamount ranging from about 0.1% to about 3% by weight of the base fluid.12. The composition of claim 1 wherein the treatment fluid comprises aviscosifier that comprises a polysaccharide.
 13. The composition ofclaim 12 wherein the viscosifier is included in the treatment fluid inan amount ranging from about 0.1% to about 1.0% by weight of the basefluid.
 14. The composition of claim 1 wherein the partiallydepolymerized starch derivative is a partially depolymerized crosslinkedether derivative of a starch.
 15. The composition of claim 1 wherein thepartially depolymerized starch derivative comprises a crosslinked etherderivative of a partially depolymerized starch and a partiallydepolymerized crosslinked ether derivative of a starch.